The present invention generally relates to the field of large area lighting, such as lighting for sport venues. More specifically, some embodiments of the present invention relate to controlling solid state illumination for various applications including sports lighting, architectural lighting, security lighting, parking, general area, interior, larger area and others.
LED lighting has many potential advantages for use in large area lighting. These benefits may include long life, efficient lighting, high intensity lighting, variability, etc. Optimizing these benefits is one goal of the lighting designer which would be facilitated by being able to measure operational status of LEDs.
Several known conditions affect normal LED operation. First, light output from LEDs normally varies as a function of junction temperature. During normal operation, LED junction temperature begins at ambient temperature, then increases until after some elapsed time period when thermal equilibrium is attained. During this elapsed time period, as junction temperature increases, output lumens per input watt decrease, which normally results in decreased fixture lumen output, since LED drivers typically provide a constant current level regardless of ambient temperature or LED temperature. Thus an LED fixture typically provides the most light when first powered on, and decreases in output as it warms up until it reaches thermal equilibrium.
Local climatic conditions also affect LED operation. A light being operated in cooler conditions will start at a lower temperature, initially put out a greater amount of light, and take longer to warm up to thermal equilibrium. Conversely, a light being operated in warmer ambient conditions will initially not deliver as much light, and will not take as long to reach thermal equilibrium.
For example, in the case of an LED fixture having a fixed power of 100 watts (W), operating in “normal” ambient conditions—possibly 70° F.—in order to achieve 30 foot candles (fc) illumination at steady-state conditions, it will provide much more than 30 fc, possibly on the order of 30% more, when it is cold and is first turned on. If the current could be reliably controlled, it might be possible to operate the fixture at 70 watts initially, gradually increasing the power as the fixture approached thermal equilibrium. Thus, for a time, the fixture would operate at reduced power, thereby reducing operating cost and reducing degradation of the LEDs.
If the same light is operated at low ambient temperatures, such as cold outdoors, ice rink, etc., a way to control current while maintaining the desired illumination level might make it possible to operate at 50 W initially and still provide 30 fc illumination.
If the same light is operated at high ambient temperatures, e.g. possibly desert conditions, the same lamp might operate at 90 watts initially for a 30 fc output. From the initial higher starting temperature, temperature will rise rapidly and output will decrease rapidly since heat is lost less quickly in higher ambient temperatures. Thus wattage required to maintain 30 fc will increase rapidly and lumen output per watt will decrease accordingly. Also, the thermal equilibrium point will be higher, which would typically reduce light output below the desired level, since the LEDs would be operating at a higher steady-state temperature. Thus a way to control current while maintaining the desired illumination level might make it possible to compensate for the operational differences and still provide 30 fc illumination. However in high ambient temperatures, and for LEDs operated at relatively high power levels, there is a risk of operating at an unacceptably high junction temperature, which can result in decreased life expectancy or premature failure.
Therefore, a way to manage LED fixtures and/or light sources which would reduce or eliminate the variance between initial and steady-state operation and/or compensate for the additional variance of ambient conditions would be highly desirable.
Furthermore, LEDs experience lumen loss, which is a gradual reduction over time in their ability to produce light. The rate of lumen loss is related to the junction temperatures and currents applied over time. Lumen loss is greater when LEDs are operated at higher temperatures and at higher currents. Thus reducing junction temperature and/or operating current for a portion of the operating time will reduce the degradation of the LED, extending its useful life. Thus, there is room for improvement in the art.
LED manufacturers typically provide information about an LED product only under limited operating conditions. For example, they may supply a comparison of forward voltage, current, and lumen output at 25° C. Since most LED fixtures will not operate at a steady temperature of 25° C., much more information about LED performance in situ would be of great benefit in the industry. Therefore, the ability to characterize LED light sources with regard to operational conditions and states is very desirable. This particularly includes information regarding lumen output and potential failure conditions, junction temperature vs. current vs. forward voltage
LEDs for area lighting are normally operated in fixtures containing multiple LEDs. These multiple LEDs are often connected in series ‘strings’ which can make fixture design and control more economical or provide better lighting. However, this introduces additional components into the operating circuit which can make it more difficult to observe LED operational status. Methods to account for these additional components as a part of observing light source and fixture status would be highly beneficial in the industry.
It is therefore a principle object, feature, advantage, or aspect of the present invention to improve over the state of the art or address problems, issues, or deficiencies in the art.